The present invention is directed to aqueous ink jet ink compositions for use with commercial offset media and offset ink.
In recent years, computer printer technology has evolved to a point where very high resolution images can be transferred to various media, including papers of different types. One particular type of printing involves the placement of small drops of a fluid ink onto a surface in response to a digital signal. Typically, the fluid ink is placed or jetted onto the surface without physical contact between the printing device and the surface. The specific method for which the ink is deposited onto the printing surface varies from system to system. However, two major methods include continuous ink deposit and drop-on-demand ink deposit.
With regard to continuous printing systems, inks used are typically based on solvents including methyl ethyl ketone and/or ethanol. Essentially, continuous printing systems function as a stream of ink droplets are ejected and directed by a printer nozzle. The ink droplets are directed additionally with the assistance of an electrostatic charging device in close proximity to the nozzle. If the ink is not used on the desired printing surface, the ink is recycled for later use. With regard to drop-on-demand printing systems, the ink jet inks are typically based upon water and glycols. Essentially, with these systems, ink droplets are propelled from a nozzle by heat or by a pressure wave. Additionally, all of the ink droplets are used to form the printed image and are ejected when needed.
In general, ink jet inks are either dye- or pigment-based. Dye-based inks typically use a liquid colorant that is usually water-based to turn the media a specific color. Because of their makeup, dye-based inks are usually not waterproof and tend to be more affected by UV light. This results in the color fading or changing over time. For optimum performance, this type of ink has often required that the proper media or substrate be selected in accordance with the application. In many circumstances, if the media is too dense or hydrophobic, the ink has difficulty penetrating and beads on the surface. Conversely, if the media is too absorbent, the dot gain is too high creating a blurred image.
Pigmented inks typically use a solid colorant to achieve color. In many cases, the line quality and accuracy of plots produced by pigment-based inks are usually superior to that of dye-based inks. With pigmented inks, solid particles adhere to the surface of the substrate. Once the water in the solution has evaporated, the particles will generally not go back into solution, and are therefore more waterproof. In addition, pigmented inks are much more UV resistant than dye-based inks, meaning that it takes much longer for noticeable fading to occur.
Though pigmented inks, in some areas, exhibit superior characteristics, dyes tend to run cleaner, provide better yield, offer better particle size, and are easier to filter. Thus, dye based inks have been more often used for common applications. Additionally, dye-based inks have tended to be more chromatic and provide more highly saturated colors.
There are several reasons that ink jet printing has become a popular way of recording images on surfaces, particularly paper. Some of these reasons include low printer noise, capability of high speed recording, and multi-color recording. Additionally, these advantages can be provided at a relatively low price. However, though there has been great improvement in ink jet printing, accompanying this improvement are increased printing demands, e.g., higher speed, higher resolution, full color image formation, etc. As such, there are several features to consider when evaluating a printer ink in conjunction with a printing surface or substrate. Such features include edge acuity and optical density of the image on the surface, dry time of the ink on the substrate, adhesion to the substrate, lack of deviation of ink droplets, presence of all dots, resistance of the dried ink to water and other solvents, long-term storage stability, and long-term reliability without corrosion or nozzle clogging. Though the above list of features provides a worthy goal to achieve, there are difficulties associated with satisfying all of the above features. Often, the inclusion of an ink component meant to satisfy one of the above characteristics can prevent another characteristic from being met. Thus, most commercial inks for use in ink jet printers represent a compromise in an attempt to achieve at least an adequate response in meeting some or all of the above listed requirements.
Papers used for ink jet printing have typically included high-quality or wood-free papers designed to have high ink absorptivity or papers having a coated porous surface. These papers are functionally good for ink jet printing because the inks may be absorbed readily and dry quickly. However, such papers often do not allow for a crisp or sharp image.
Conversely, with commercial offset paper, a nonporous smooth surface may provide a good printing surface for a crisp image. However, commercial offset coated papers are significantly different than office plain papers or photo/glossy papers specifically designed for ink jet media. Typically, with commercial offset papers, the smooth non-porous surface is comprised of a coating which requires more time for aqueous fluids to penetrate than standard paper. This is because diffusion-type adsorption must generally occur with offset papers as compared with capillary-type absorption which typically occurs with respect to standard office paper and some ink jet specialty papers. Additionally, offset coatings contain polymers that are more hydrophobic, e.g., styrene-butadiene based, than paper coatings specifically designed for ink jet ink, e.g., water-soluble polymers such as polyvinyl alcohol. Thus, because offset coatings are typically hydrophobic, have poor penetration, and are smooth and nonporous, these coatings tend to interact poorly with water-based inks. In addition, classic ink jet solvents such as glycols and diols tend to perform poorly on these coatings, showing long dry times and poor spreading characteristics.
The apparent incompatibility between offset media/ink and water based ink jet inks stems from the fact that offset media such as commercial offset paper was developed primarily for use with oil-based inks. For example, coated offset media often includes a hydrophobic component such as latex binder and/or various hydrophobic polymers. To illustrate, such polymers used in offset media can include polymers, copolymers, and/or terpolymers selected from the group consisting of polystyrene, polyolefins (polypropylene, polyethylene, polybutadiene), polyesters (PET), polyacrylate, polymethacrylate, and poly(maleic anhydride).
Because commercial offset paper provides a smooth surface for printing and would provide a convenient and inexpensive alternative to specialty papers, it would be useful provide aqueous based ink jet inks which can be used with commercial offset media, including papers and offset inks. Such formulations would be particularly useful if they exhibited a reduction in ink dry out in ink jet nozzles. Additionally, these ink jet inks would also be desirable if they exhibited printing properties on offset media including excellent text and area fill, minimal coalescence in half tone images, excellent optical density (OD) and edge acuity, good water fastness, good smudge and rub resistance, and good lightfastness.
The present invention is drawn to aqueous based ink compositions for ink jet printing on offset media and offset ink. One embodiment comprises effective amounts of an ink colorant and a nonionic surfactant having an HLB value from about 4 to 14. Optionally, additional nonionic surfactants, solvents, and binders can be added. Another embodiment comprises an effective amount of an ink colorant, at least two nonionic surfactants, each being present at from about 0.01% to 10% by weight, and an effective amount of at least one polymeric binder, such as an acrylate binder.
Before the present invention is disclosed and described, it is to be understood that this invention is not limited to the particular process steps and materials disclosed herein because such process steps and materials may vary somewhat. It is also to be understood that the terminology used herein is used for the purpose of describing particular embodiments only. The terms are not intended to be limiting because the scope of the present invention is intended to be limited only by the appended claims and equivalents thereof.
It must be noted that, as used in this specification and the appended claims, the singular forms xe2x80x9ca,xe2x80x9d xe2x80x9can,xe2x80x9d and xe2x80x9cthexe2x80x9d include plural referents unless the content clearly dictates otherwise.
xe2x80x9cSurfactantxe2x80x9d is a compound that contains a hydrophilic and a hydrophobic segment. Thus, when a surfactant is added to water or some other solvent, the surface tension of the system can be reduced. In general, surfactants can be used for several purposes including wetting, emulsifying, dispersing, foaming, scouring, or lubricating a system.
xe2x80x9cHLBxe2x80x9d or xe2x80x9cHydrophilic/Lipophilic Balancexe2x80x9d is a way of classifying surfactants. Specifically, the HLB scale ranges from 0 to 40 wherein the products with a low HLB are more oil soluble and products with a higher HLB are more water soluble. The HLB is a numerically calculated number based on the surfactants molecular structure, thus, it is not a measured parameter.
With this in mind, an aqueous ink composition for ink jet printing on offset media and offset ink is disclosed comprising effective amounts. of ink colorant and a nonionic surfactant having an HLB value from about 4 to 14. In one embodiment, an effective amount of a second nonionic surfactant can be added to the composition. The HLB value of the second nonionic surfactant can be any functional value. However, it is preferred that the second nonionic surfactant also have an HLB value from about 4 to 14.
If one nonionic surfactant is used, the nonionic surfactant can be present at from 0.01% to 10% by weight, preferably from about 0.01% to 5% by weight, and most preferably from about 0.01% to 2% by weight. However, if two or more nonionic surfactants are used, each nonionic surfactant can be present at within these ranges. Suitable nonionic surfactants for use can include alkoxylated octylphenols, alkyl phenoxypoly(ethleneoxy)ethanols, silicone glycol copolymers including polyalkylene oxide-modified polydimethylsiloxanes, alkoxlyated tetramethyl decyndiols, alkoxylated trimethylnonanols, polyoxyethylene ethers, ethylene oxide/propylene oxide copolymers, fluorosurfactants, and nonionic alkoxylated surfactants. Preferred alkoxylates for above are ethoxylate and propoxylates.
Nonionic surfactants can be obtained from several sources, including those with the tradenames TRITONS(trademark), IGEPALS(trademark), SILWETS(trademark), SURFYNOLS(trademark), TERGITOLS(trademark), BRIJS(trademark), PLURONICS(trademark), FLUOKADS(trademark), and ZONYLS(trademark)
As is the case with many ink jet inks, the ink colorant is preferably selected from the group consisting of pigments and dyes. However, in either case, the ink colorant should be present at from about 0.1% to 10% by weight. In one embodiment, an acrylate binder (water soluble or water dispersible acrylate polymer) or another functionally equivalent binder can be used such as an acrylic acid or a methacrylate acid including its esters. Preferably, the binder can be present at from about 0.01% to 10% by weight and a preferred molecular weight range can be from about 1,000 to 15,000.
Also, an aqueous ink composition for ink jet printing on offset media and offset ink is also disclosed comprising an effective amount of ink colorant; at least two nonionic surfactants, each being present at from about 0.01% to 10% by weight; and an effective amount of at least one binder. In this embodiment, one of the at least two nonionic surfactants can have an HLB value from about 4 to 14. In another embodiment, two or more of the at least two nonionic surfactants can have an HLB value from about 4 to 14.
Though no specific limitation regarding the amount of ink colorant to be used (other than an effective amount) is required, it is preferred that the ink colorant be present at from about 0.1% to 10% by weight. Additionally, either pigments and/or dyes can be used in the formulation. For example, a suitable ink colorants can be the self-dispersed carbon pigment known as CABOJET(trademark) 300. Additionally, ink colorants such as those described in U.S. Pat. Nos. 5,3,56,464 and 5,709,737, the entire teachings of which are incorporated herein by reference, can also be used. In this embodiment, the binder can preferably be an acrylate binder, an acrylic acid, a methacrylate acid including its esters, and combinations thereof. JONCRYL(trademark) is one commercially available acrylate binder that is acceptable for use. Additionally, other water-insoluble monomers can be used for the binder. For example, the binder can be comprised of comonomers such as a styrene and a butyl methacrylate. Other suitable binders that can be used include polyamides, vinylalcohols, vinyl acetates, polyvinylpyrrolidones, cellulosics, and urethanes. The binder should be present at from about 0.01% to 10% by weight. Additionally, molecular weights for the binder can be from about 1,000 to 15,000. Though these inks and binders are discussed specifically, other ink colorants or binders optimized for thermal ink jet ink can also be used.
Solvents can also be added to the formulations for good results. Such solvents can include alcohols and polyhydroxylated solvents including glycerols, glycols, glycol ethers, pyrrolidones, and combinations thereof. When using one of these or other solvents, the solvent should be present at from 0.5 to 50% by weight. Additionally, as stated previously with respect to other embodiments, the nonionic surfactant(s) can be selected from the group consisting of alkoxylated octylphenols, alkyl phenoxypoly(alkyleneoxy)ethanols, silicone glycol copolymers including polyalkylene oxide-modified polydimethylsiloxanes, alkoxlyated tetramethyl decyndiols, alkoxylated trimethylnonanols, polyoxyethylene ethers, ethylene oxide/propylene oxide copolymers, fluorosurfactants, and nonionic alkoxylated surfactants.
As water is the major component in typical ink jet ink formulations, in the prior art, offset coatings have tended to interact poorly with aqueous inks. In addition, classic ink jet solvents such as glycols and diols tend to perform poorly alone on these coatings, showing long dry times and poor spreading characteristics. Prior to the present invention, offset media was typically printed on using water insoluble solvents (xylene or toluene) and oils (linseed or soybean) in the ink formulation. Because these components are incompatible with water, they are difficult to jet out of an ink jet pen. By adding the nonionic surfactants to aqueous based inks as prescribed herein, dry time and spreading on the offset media and offset ink can be improved. Additionally, such formulations can be used in an ink jet pen with good reliability. The use of nonionic surfactants as disclosed herein also reduces the amount of heating required to dry inks. As offset papers are often hydrophobically coated, massive amounts of heat may otherwise be required to dry inks, leading to the cost and size of a given printing device to be increased. By improving the penetration of the ink into the coatings through the use of nonionic surfactants, less heat is required to remove the fluid at the surface of the paper. Thus, reduction of ink transfer from sheet to sheet is effectuated.
Another advantage of the present invention is cost savings and convenience to consumers. Commercial offset paper is often much less expensive and are much more available than specialty media paper designed specifically for certain ink jet inks. As the ink jet inks of the present invention have decreased dry time on commercial offset paper, overall printing speed can also be maintained at an acceptable level.